Genetic increases in growth do not lead to trade-offs with ecologically important litter and fine root traits in Norway spruce

The genetic composition of many forests across the world is being altered through the introduction of genetic material selected and bred for superior production qualities. Growth strategy and allocation theories predict that introducing genetic material with faster growth rates into managed forest populations could result in tradeoffs that influence the expression of other traits of ecological importance to the tree and its associated communities and ecosystem processes. We assessed variation in tree traits among ten full-sibling and four open-pollinated progenies of Norway spruce (Picea abies L. Karst.) growing within a 38 year old common garden in Sävar, Sweden; namely fine root and litter carbon, nitrogen, lignin, starch and condensed tannin concentrations as well as the specific leaf area (SLA) and root tissue density (RTD). We first tested whether these traits varied among spruce progenies, and secondly, if they exhibited significant relationships with tree growth expressed as diameter at breast height (DBH). Significant variation was detected in the DBH of progenies, with a three-fold difference between the slowest and fastest growing progenies. Although progenies exhibited significant variation in SLA, RTD, as well as needle litter and fine root condensed tannin concentrations, only SLA exhibited a significant relationship with DBH. These findings suggest that while a shift to faster-growing genetic material in managed forests may not necessarily result in tradeoffs with the expression of other ecologically important traits, the origin of planted genetic material and increased growth itself is likely to impact the quality and quantity of organic matter entering soils.